"""Parsing the matrixes in a PDF file."""

from __future__ import annotations

from logging import getLogger

from pikepdf import Matrix, Operator, Page, parse_content_stream

logger = getLogger(__file__)
OPERATOR_CM = Operator(
    'cm'
)  # "Concatenate Matrix": Changes the CTM (Current Transformation Matrix)
OPERATOR_DO = Operator('Do')  # "Draw Object":
OPERATOR_STACK = Operator('q')  # Stores the CTM to a stack
OPERATOR_POP = Operator('Q')  # Restores the previous CTM


class MatrixStack:
    """Tracks the CTM (current transformation matrix) in a PDF content stream.

    The CTM starts as the initial matrix and can be changed via the 'cm'
    (concatenate matrix) operator --> CTM = CTM x CM (with CTM and CM
    being 3x3 matrixes). Initial matrix is the identity matrix unless overridden.

    Furthermore can the CTM be stored to the stack via the 'q' operator.
    This save the CTM and subsequent 'cm' operators change a copy of that CTM
    --> 'q 1 0 0 1 0 0 cm'
    --> Copy CTM onto the stack and change the copy via 'cm'

    With the 'Q' operator the current CTM is replaced with the previous one from the
    stack.

    Error handling:
    1. Popping from an empty stack results in CTM being set to the initial matrix
    2. Multiplying with invalid operands sets the CTM to invalid
    3. Multiplying an invalid CTM with a valid CM results in an invalid CTM
    4. Stacking an invalid CTM results in a copy of that invalid CTM onto the stack
    --> All operations with an invalid CTM result in an invalid CTM
    --> The CTM is valid again when all invalid CTMs are popped off the stack
    """

    def __init__(self, initial_matrix: Matrix = Matrix.identity()) -> None:
        """Initializing the stack with the initial matrix."""
        self._initial_matrix = initial_matrix
        self._stack: list[Matrix | None] = [self._initial_matrix]

    def stack(self):
        """Copying the current CTM onto the stack."""
        self._stack.append(self._stack[-1])

    def pop(self):
        """Removing the current CTM from the stack.

        The stack is not permitted to underflow. If popped too many times, the CTM
        is set to the initial matrix. Some PDFs contain invalid content streams
        that would result in an underflow, therefore the initial matrix is used
        as a safe fallback.
        """
        assert len(self._stack) >= 1, "can't be empty"
        if len(self._stack) == 1:
            self._stack = [self._initial_matrix]
        else:
            self._stack.pop()

    def multiply(self, matrix: Matrix):
        """Multiplies the CTM with `matrix`. The result is not returned."""
        if self._stack[-1] is None:
            return
        else:
            self._stack[-1] = self._stack[-1] @ matrix

    def invalidate_current_transformation_matrix(self):
        """Registers the occurence of an invalid CM.

        See `# Error handling` for further informations.
        """
        self._stack[-1] = None

    @property
    def ctm(self) -> Matrix | None:
        """Returns the current transformation matrix or `None` if it's invalid."""
        return self._stack[-1]


def get_objects_with_ctm(
    page: Page, initial_matrix: Matrix = Matrix.identity()
) -> list[tuple[str, Matrix]]:
    """Determines the current transformation matrix (CTM) for each drawn object.

    Filters objects with an invalid CTM.
    """
    objects_with_ctm: list[
        tuple[str, Matrix]
    ] = []  # Stores the matrixes and the corresponding objects
    matrix_stack = MatrixStack(initial_matrix)
    for inst in parse_content_stream(page):
        operator, operands = inst.operator, inst.operands
        if operator == OPERATOR_STACK:
            matrix_stack.stack()

        elif operator == OPERATOR_POP:
            matrix_stack.pop()

        elif operator == OPERATOR_CM:
            try:
                matrix_stack.multiply(Matrix(*operands))
            except TypeError:
                logger.debug(f"malformed operands for `cm` operator: {operands}")
                matrix_stack.invalidate_current_transformation_matrix()

        elif operator == OPERATOR_DO:
            name = str(operands[0])  # Name of the image (or other object)
            if matrix_stack.ctm is not None:
                objects_with_ctm.append(
                    (name, matrix_stack.ctm)
                )  # Explicit copying the CTM
            else:
                logger.debug(
                    f"skipping `Do` operator due to invalid CTM for object: {name}"
                )

    return objects_with_ctm
